自制与市售酸奶贮藏过程品质变化对比研究

[目的]对比自制酸奶与市售酸奶在贮藏期间的品质变化。[方法]通过乳酸菌活菌数、酸度、pH值等指标，先探究自制酸奶在发酵过程中的品质变化，后与市售酸奶进行对比研究。[结果]自制酸奶过程中，发酵开始3 h后，随着乳酸菌发酵产物乳酸的累积，酸度上升、pH值下降，乳酸菌活菌数大幅度上升。发酵开始7 h后，乳酸菌总数开始下降，酸度的增加趋势和pH的降低趋势都有所减缓。在贮藏阶段，随着贮藏时间的增长，各种酸奶品质变化基本相同，乳酸菌含量先升后降，pH值下降，酸度上升。在4℃贮藏条件下，品质变化小于25℃。[结论]冷藏处理下酸奶的品质下降更慢，在自制或者购买酸奶时应该尽可能选择冷藏处理，开盖后尽快饮用完。两种酸奶具有不同的特点，消费者可以根据需求进行选择。总之，本研究为酸奶的安全贮藏提供参考依据。

A Comparative Study of the Quality Changes in the Storage Process of Homemade and Commercially Available Yogurt

[Objective] To study and compare the quality changes of homemade yogurt and commercial yogurt during storage. [Method] The quality changes of homemade yoghurt during fermentation were studied by means of lactic acid bacteria count,acidity and pH,and then compared with commercial yoghurt. [Result] In the process of homemade yogurt,3 h after fermentation,with the accumulation of lactic acid, the acidity increased,the pH value decreased,and the viable number of lactic acid bacteria increased significantly. After 7 h fermentation,the total number of lactic acid bacteria began to decrease,and the increasing trend of acidity and the decreasing trend of pH slowed down. In the storage stage,with the increase of storage time,the quality changes of all kinds of yogurt are basically the same,the content of lactic acid bacteria first increases and then decreases,the pH value decreases,and the acidity increases. Under the condition of 4℃ storage,the quality change is less than 25℃. [Conclusion]The quality of yoghurt decreases more slowly under refrigerated treatment. When making or buying yoghurt,we should choose refrigerated treatment as much as possible and drink it as soon as possible after opening the cover. The two kinds of yogurt have different characteristics,and consumers can choose according to their needs. In conclusion,this study provided a reference for the safe storage of yogurt.